What details suggest madness in the story and its climax and how is the plot resolved?"The Masque of the Red Death"

In Edgar Allan Poe's gothic tale, "The Masque of the Red
Death," Prince Prospero's plan to stave off the plague by sequestering himself and his
guests in an ancient abbey where they "girdled" in by a lofty wall that has iron gates
certainly seems rather illogical.  For, it is as though the prince fortifies himself and
his guests against a tangible enemy.  Even security guards are employed to prevent
unwanted visitors. The discrepancies in the prince are indicated by the narrator who
shows the contrast between Prospero's personality and the
situation:

But
the Prince Pospero was happy and dauntless and sagacious.  When his dominions were half
depopulated, he summoned to his presence a thousand hale and light-hearted friends from
among the knights and dame of his court....It was a voluptuous scene, that
masquerade.

Like the Roman
saying, "Eat, drink, and be merry, for tomorrow we may die," the court and its
prince revel in the fete as they disguise themselves in luxurious and full gratification
of their senses (voluptuous), disregarding completely the imminent danger.  That the
festivities are engaged in an old, dark, and mysterious building in which the lighting
creates bizarre impressions with the vivdly blue, purple, green, orange, and black rooms
and decor seems mad, indeed.  Poe's narrator remarks on this
decor:

But,
in spite of these things, it was a gay and magnificent revel.  The tastes of the duke
were peculiar.  He ahd a fine eye for colors and effect.  He disregarded the decora of
mere fashion.  His plans were bod and fiery, and his conceptions glowed with barabaric
luster.  There are some who would have thought him mad.  His followers thought that he
was not.  It was necessary to hear and see and touch him to be sure that he was
not.

However, despite their
mad gaiety, Prince Prospero and his guests cannot bar the Red Death from becoming their
unwanted guest, with a "vesture...dabbled in blood."  And, when the Red Death, whose
face was "besprinkled with the scarltet horror," enters Prince Prospero watches him walk
among the dancers, he was seen "to be convulsed...with a strong shudder...,but, in the
next, his brow reddened with rage.  The prince asks, "Who dares?...Seize him and unmask
him."  At these words the climax begins and some of the guests started forward, but
suddenly stop as the intruder passes close to the prince.  Finally, the prince,
"maddening with rage and the shame of his own momentarily cowardice, rushes forward with
a drawn dagger in his hands.  In the height of the climax, Prince Prospero raises his
dagger and approaches just as the monster suddenly confronts his
assailant,

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There was a sharp cry--and the dagger dropped
gleaming upon the carpet of the black apartment, and instantly...fell prostrate in death
the Prince Prospero.

Only
after Prospero falls is the presence of the Red Death
acknowledged.

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He had come like a thief in the night.  And
one-by-one dropped the revelers in blood-bedewed halls of their revel, and died each in
the despairing posture of his fall.  And the life of the ebony clock went out with that
of the last of the gay.

The
revelers all succumb and die; the clock even goes out.  The Plague has eradicated
all--this is the denouement.